The JNR freight car classification system was made up of a number of katakana characters indicating type, capacity, and optionally other details, along with a serial number. The katakana class designation took the form of (X)YZ, where X was an optional superscript prefix indicating any necessary extra details; Y indicated the type, and Z indicated the car's capacity.
* テ (Te): refrigerator cars with ceiling-mounted ice bunkers
* ナ (Na): refrigerator cars without ice bunkers
* ワ (Wa): multi-use cars (boxcar-substituting open cars)
* コ (Ko): open cars of 15t/17t capacity; tank cars 12m or less in length
* ス (Su): open cars of 15t/18t capacity
* オ (O): open cars of 36t capacity or greater; tank cars 16m or greater in length; hoppers 12m or greater in length
* ハ (Ha): boxcars for palletised cargo of 15t capacity
* ロ (Ro): cars with maximum speed of 65km/h or less
* ア (A): aluminum tank cars
* ワ (Wa): boxcars, wood-lined
* テ (Te): boxcars, iron-lined/waterproof
* ス (Su): boxcars, steel-lined
* カ (Ka): stock cars
* ツ (Tsu): ventilated boxcars
* ポ (Po): pottery cars
* レ (Re): reefers
* ウ (U): pig transport cars
* ト (To): gondolas
* ク (Ku): auto transporter (from 1965; prior to 1965, these considered covered cars)
* シ (Shi): heavy goods transporter
* チ (Chi): flatcars
* コ (Ko): container flats (from 1966)
* リ (Ri): gravel cars
* タ (Ta): tank cars
* ミ (Mi): water cars
* ホ (Ho): hoppers
* セ (Se): coal cars
* ヨ (Yo): guards vans
* エ (E): rescue/emergency cars
* キ (Ki): snow-removal equipment
* ケ (Ke): scale test cars (after 1966; prior to 1966, コ)
* サ (Sa): work vehicles
* ソ (So): cranes
* ヒ (Hi): idler cars
* ヤ (Ya): test cars, rolling laboratories, etc.
* フ (Fu): car with brakeman's compartment. Placed after capacity indicator, e.g. ワフ - wood-lined boxcar with guard's compartment.
* none - under 13t
* ム (Mu): 14t-16t
* ラ (Ra): 17t-19t
* サ (Sa): 20t-24t
* キ (Ki): over 25t